Looks like I am getting ready to own a 4WD bullnose. A mostly unmolested '81 F150 with the 300 6-banger. Current owner indicates the major problem is a vapor lock issue. I find this hard to believe it is really vapor lock, but maybe? I've been driving Fords for the last 40 years and never had vapor lock on any of my rides, including a 250CID 6-banger. Fuel delivery issue, sure, vapor lock, I doubt it. Thoughts?

 

If it only does it on very hot summer days, possibly. The ethanol fuel they use now is very prone to vapor lock. I had a stock 2.8 v6 equipped bronco II, and it had vapor lock problems. I know it did not leave the factory that way. It was a simple to fix though, a small electric pump mounted on the frame near the fuel tank.

It all depends on the symptoms and when it does it.

 

Please try to find out under what conditions “vapor lock” occurs. It’s a very broad term with several possible scenarios behind the problem.

Lots of helpful info in this thread:

https://www.ford-trucks.com/forums/1...apor-lock.html

 

Welcome to the tractor motor group
You are right as the only time I have any kind of fuel / heat issue is when it is vary hot out and I sit with the AC on for 10+ min.
I can see the factory temp gauge climb when sitting and when I start to move the truck will stumble a bit but then be ok.
I keep forgetting to look at my AFR gauge to see what that is reading when this happens, last time it was with a 20' enclosed trailer.

I would start by replacing all rubber fuel line, it takes 5/16 NOT 3/8 as I could not get that to seal even with 2 clamps.
Change any fuel filter and maybe a carb rebuild / clean just so you know it is in good health.

Now the factory log exhaust has a valve that lets HOT exhaust gases heat the bottom of the log intake manifold.
Sometimes this valve gets rusted where it is blowing the HOT gases on the intake manifold so you need to check this.
Depending were you live you might be able to leave it open all the time so no heat is on the intake manifold.

If you have to replace the log exhaust manifold you may want to look into the 87> EFI Tri Y manifolds and factory Y pipe.
Not this does bring on a few things like no heat to the intake manifold but can be over come pretty easy and no hot air choke tubes that can also be over come pretty easy.
I have done both and still using the factory log intake manifold / carb with the EFI exhaust manifolds.

As Karl brought up if it just shuts off like the key was turned off I would look at the ICM, the box on the inner fender well.
It heats up and no more spark then when it cools off you have spark. Just getting out and opening the hood is enough to cool it off at times.
Good luck and keep us posted
Dave ----

ps we want to see pictures too

 

Make certain the seller knows the difference between vapor lock and carb icing. Vapor lock in the middle of the winter?

 

I had an 81 F250 C-series motorhome with a 300 six and C-6 transmission. At the time I lived in Denver and on the weekends we took off for the mountains anytime it was 80 degrees or more we could not make it to the tunnels on I-70. I would have to pull off and let things cool off. Engine temp was always fine. Altitude brings everything to a boil quickly, plus hot engine oil from a long pull in the fuel pump, plus the air being less dense for overall cooling. Electric fuel pump between tank valve and engine fuel pump was the fix.

 

If converting from mechanical to electric be sure to bypass and replace the mechanical pump with a block off plate. The mechanical pump will continue to work itself to death long after the diaphragm is breeched with the real chance of contaminating your oil with fuel. But even if bypassed the pump can come apart and damage your engine. One poster had the mechanical arm come loose and be banged through the oil pan causing a leak in the pan. Replace with block off plate at your earliest convenience.

 

Interesting. Appreciate the responses. I read through most all these links, and that's a lot, it comes back to most "resolving" the issue with an electric pump. I'm going to reserve my opinion until I have 1st hand experience with the subject truck. However, those who wired in a pump might want to consider what might happen in a wreck where that cheap chinese pump just keeps humming along feeding the fire that hopefully only consumes the truck without you in it.

The fuel quality issue is plausible, never thought of that, and I agree it is total crap, but then why is this issue not significantly more prevalent? I have numerous, older, carburetor equipped engines fed with a mechanical pump that do not have issues. It's not from lack of heat certainly, as we have multiple 100 degree days in the summer.

I might be insane(wife concurs), but I relish the thought of tackling issues such as these, I always have.
Thank you.

 

Equipment does not seam to be effected from the new fuel blend only cars / trucks and only if they have a carb.
The only car / truck that I have with a carb in my 81 F100 everything else is EFI even my garden tractor I use to cut the grass and that takes between 3 to 4 hours to cut.
Dave ----

 

It's great to do research, but I would not come to any conclusions until you get it and mess with it and do a little troubleshooting. You get the best deals on vehicles buying them from someone who does not know what they are talking about.